This invention relates to a ballistic modifier for use in a double base propellant mixture in which a mesa burning effect is desired. Processes for making double base propellants exhibiting a mesa effect by solvent means incorporating said ballistic modifier are also provided by the invention.
At a given temperature, the burning rate of a propellant is in direct relationship to the pressure to which it is exposed. Mathematically the relationship is expressed as: r = cp.sup.n where r is the burning rate, p is the pressure and c and n are constants determined by the type of propellant used.
Where n equals zero or some negative value the burning rate will exhibit a plateau or mesa effect. Propellants exhibiting either a plateau or mesa effect give a constant or decreasing burning rate and as a result a steady thrust. Thus vehicles using such propellants exhibit flatter and more ascertainable trajectories.
In the past propellants with a desired mesa burning rate were produced by the mixture of a nitrocellulose-nitroglycerin double base propellants with lead and copper salts of aromatic acids and various plasticizers and stabilizers. The mixture was accomplished by a solventless process in which the water-wet nitrocellulose and a mixture of nitroglycerin in a plasticizer was added and was thoroughly mixed to insure uniformity.
The mixture was filtered or centrifuged to remove most of the water and the resulting paste was aged for several days at a warm temperature. After aging ballistic modifiers were added to the paste which was blended and then milled to a homogeneous colloid on a heated differential rolling mill. The colloid was even-speed milled to produce carpet rolls which could then be extruded, sized or embossed.
Although acceptable, this type of process required extensive machinery, was not economic, and inherently lacked reproducibility as to ballistic modification thus giving rise to varying mesa values in each particular batch of propellant.
Secondly, the process while producing a propellant with good ballistics, that is, mesa burning rate, did not produce a propellant with desired physical strength.
The present invention is an organo-metallic salt complex suitable for use as a ballistic modifier and which allows the production of propellants by a solvent or a solvent/solventless process.
It is an object of this invention to provide an improved ballistic modifier.
A further object of this invention is the preparation of the organo-metallic ballistic modifier.
A still further object of this invention is to provide a solvent process and a solvent/solventless process which produces a propellant with both desirable mesa effects and increased physical strength incorporating such modifier.
Yet another object of this invention is to provide a solvent process and a solvent/solventless process for producing mesa type propellants which is more efficient and economical than previous solventless type processes.
Yet another object of this invention is to provide a solvent process and a solvent/solventless process for producing mesa type propellants which have a high degree of reproducibility as to a specific mesa burning rate.
Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description.
The present modifier is porduced independently of the propellant mix by reacting about equal parts by weight of normal lead beta resorcylate and basic cupric salicylate in a water solution at an elevated temperature. Upon evaporation of the water, a deep green salt complex remains as a residue.
In addition to the aforementioned percentages by weight, the modifier may be produced by about the following weight percentages of the two salts: normal lead beta resorcylate (85-15 percent) and basic cupric salicylate (15-85 percent). Optimum yield of the modifier complex occurs however when the two salts are added in equal parts.
The temperature of the water solution may range from 180.degree. F to 212 .degree. F with no appreciable change in yield.
The same modifier complex may be produced by substituting an alcohol solution totally or in part for the water solution.
Alcohols that have been found effective include methanol, ethanol, isopropanol, and tertiary/butyl/alcohol.
The modifier once formed as a residue may be used in a solvent process or a solvent/solventless process for the manufacture of propellants producing propellants exhibiting a mesa burning rate.
The solvent and solvent/solventless processes for the manufacture of propellants consist essentially of forming mixtures of water-wet nitrocellulose and ballistic modifier and nitroglycerin with various stabilizers and plasticizers. The mixtures are then combined, colloided, screened, extruded and dried to produce homogeneous propellant strands.
Stabilizers which have been found effective consist of any compound or mixture of compounds which prevent the decomposition of nitrocellulose while not interfering with the ballistic or structural properties of the propellant. Examples include: diphenylamine, 2 nitrodiphenylamine, ethyl centralite and n-methyl p-nitroaniline.
Examples of plasticizers which may be used to advantage include nitroglycerin, diethylene glycol dinitrate, triethylene glycol dinitrate, dinormal propyl adipate, 1,2,3 butanetriol trinitrate, 1,2,4 butanetriol trinitrate and trimethylolethane.
Other additives may be added to produce certain desired effects for example: candelilla wax as an extrusion lubricant and carbon black as an opacifying agent.
Colloiding mediums which have been found effective consist of any agent capable of colloiding gun cotton. Examples include: acetone, ethyl acetate, methyl ethyl ketone and ethylene glycol monomethyl ether.
By inclusion of the step of over-colloiding in the propellant's manufacture, that is, the addition of one of the colloiding solvents in excess, mesa ballistic characteristics are enhanced.
By use of these processes in the propellant's manufacture, the desired mesa effect is achieved and good physical characteristics, e.g., increased strength are imparted to the propellant.
Further, by use of solvent and solvent/solventless processes, the degree of colloiding during mixing may be rigidly controlled. This, in time, results in a high degree of reproducibility from batch to batch.
With the elimination of several operations inherently found in the solventless process, the cost and time savings would be substantial.
Although it is not intended that the invention be limited thereto, there is set forth herein below for purposes of illustration, examples of how the ballistic modifier may be produced and solvent and solvent/solventless processes incorporating such ballistic modifier producing propellants which exhibit a mesa burning rate while retaining superior physical strength.